| Summary: | Aerosol optical depth (AOD), a key aerosol property used in climate models and air quality studies, is primarily measured by satellite-based instruments such as NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) and NASA’s Multi-angle Imaging SpectroRadiometer (MISR). These satellite-based measurements, however, have higher uncertainties over complex, mountainous terrain. Due to these geographically dependent uncertainties, it is imperative to validate the satellite data with measurements from ground-based instruments such as NASA’s Aerosol Robotic Network (AERONET), but spatial coverage over mountainous terrain within the United States and Africa, for example, is sparse. Networks of inexpensive handheld sunphotometers have the unique potential to complement AERONET and increase the spatial coverage of AOD measurements, but the usefulness of these measurements is heavily dependent on instrument design, adequate calibration, and characterization of instrument performance against reference standards such as the CIMEL sunphotometers used at AERONET sites. Dr. James Sherman’s research group at Appalachian State University previously developed handheld microcontroller-based sunphotometers utilizing filtered photodiodes, which were deployed to Botswana in 2018 for Citizen Scientist AOD measurements. These instruments demonstrated excellent agreement with AERONET-measured AOD and long-term calibration stability but were restricted by issues related to time synchronization, data transmission, reliability, and ease of use. I have designed and implemented software and hardware solutions to address these issues, including a new Global Positioning System (GPS) module to better synchronize the instrument’s time and a new measurement protocol to optimize data acquisition. In addition, I have built upon previous students’ work to improve the instrument’s troubleshooting simplicity and to develop an improved housing to accommodate the instrument’s new hardware components. Our newest generation handheld sunphotometer ...
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